1. Field
This invention relates generally to nondestructive examination transducers and, more particularly, to ultrasonic phased array transducers for inspecting components in restricted areas.
2. Related Art
A boiling water reactor (BWR) produces electrical power by heating water in a reactor pressure vessel that contains a nuclear fuel core in order to generate steam which is used to drive a steam turbine. Various components and structures in a nuclear reactor are examined periodically to assess their structural integrity and determine the need for repair. Ultrasonic inspection is a known technique for detecting cracks in nuclear reactor components. A number of the inspection areas in a nuclear reactor, such as a BWR, have limited access and, therefore, are difficult to assess using an inspection tool. A jet pump in a BWR is one such component.
The jet pump riser pipe welds are periodically inspected for cracking. The presence of cracking can diminish the structural integrity of the jet pump riser pipe and elbow; however, the jet pump riser pipe welds are difficult to access. Access to the jet pump riser pipe welds is limited to the annular space between the outside of the shroud and the inside of the reactor pressure vessel, between adjacent jet pumps. The ability to scan the pipe welds is additionally restricted within the narrow space between the jet pump riser pipe and vessel, shroud, or welded attachments such as the riser brace or restrainer brackets. The jet pump riser assembly is comprised of fillet welds in which attachments are welded to the riser pipe or butt welds in which elbows and pipes are amalgamated through welding.
Weldments including the weld and the heat affected zone adjacent to the weld are ultrasonically inspected, otherwise referred to as the “weld volume.” Cracking orientation may be of two classifications; circumferential (parallel to the weld) or axial (perpendicular to the weld). The inspection of the weld volume for the detection of circumferential and axial orientated cracking is commonly performed by a combination of scans that involve transducer rotations or a combination of transducers positioned such that the ultrasonic sound beam(s) interrogates the weldment's heat affected zone in multiple directions (clockwise, counter-clockwise and perpendicular to the weld).
Ultrasonic testing is a method of characterizing the internal structure of a test piece through the use of high frequency sound waves. The frequencies used for ultrasonic testing are many times higher than the limit of human hearing, most commonly in the range from 500 KHz to 20 MHz. High frequency sound waves are directional, and can travel through a steel medium until the beam strikes a boundary from another medium (such as a crack or void), at which point the beam is reflected back to be characterized.
Previous ultrasonic weldment inspection technology typically employed a single or dual element piezoelectric crystal transducer that generates a single beam on a specified wedge to create a predetermined angle in which the beam would travel through the medium. Multiple probes would be necessary to examine the weld volume in varying directions, angles or require the complexity of remote tooling for individual transducer rotation. Phased array probes utilized for weld inspections are advantageous as fewer transducers are needed, and more importantly they require less transducer manipulation. Phased array transducers have the advantage of being able to generate numerous ultrasonic beams from a single transducer assembly containing a row or rows of sensor elements in which each can be pulsed separately creating a single beam or multiple beams at various angles (array) in a sweeping manner in a first direction. Some phased array technology enables the transducers to steer the beam(s) generation in a second direction without rotation of the phased array transducer. The phased array sweeping and steering capabilities are driven by an ultrasonic operating system, the number of piezoelectric elements and the element's positioning within the housing.
Inspections using ultrasonic testing techniques can be difficult due to the complexity of the geometry of the object to be inspected or the limited access to the component. In such cases the transducer may be contoured to increase the coupling between the contact surface of the transducer and the component being inspected. Problems sometimes arise with the automated tooling that is used to maneuver the transducers and, more specifically, with the ability to maintain contact between the transducers and the component being examined. Maintaining contact between the flat surfaces of a transducer with the concave or convex surface of a pipe system can be challenging. Poor coupling may result in missed detection of a flaw or lack of data quality to satisfy the inspection requirements.
Furthermore, inspecting and repairing nuclear reactors, such as boiling water reactors, typically can require complex tooling in order to position or move the phased array transducer to complete the examination. Plant utilities have a desire to reduce the number of manipulator installations and removals to reduce radiological exposure as well as cost and plant outage impact. Tooling with less complexity typically has the advantage of added reliability and a smaller tooling design enables access to areas with limited proximities.
Accordingly, a new ultrasonic phased array transducer assembly is desired that is relatively small in size and uncomplicated.
Additionally, such a transducer is desired that requires less movement to fully interrogate a jet pump weld.